TEHRAN, Iran -- Iran has halted oil shipments to Britain and France, the Oil Ministry said Sunday, in an apparent pre-emptive blow against the European Union after the bloc imposed sanctions on Iran's crucial fuel exports.

The EU imposed tough sanctions against Iran last month, which included a freeze of the country's central bank assets and an oil embargo set to begin in July. Iran's Oil Minister Rostam Qassemi had warned earlier this month that Tehran could cut off oil exports to "hostile" European nations. The 27-nation EU accounts for about 18 percent of Iran's oil exports.

Targeting Britain and France appeared to be a political decision by Iran to punish the two countries for supporting tougher sanctions against Iran over its disputed nuclear program.

"Crude oil exports to British and French companies have been halted," Oil Ministry spokesman Ali RezaNikzad-Rahbar said on the ministry's website. "We have our own customers and have no problem to sell and export our crude oil to new customers."

Britain's Foreign Office declined comment, and there was no immediate response from French officials.

The European Commission said last week that the bloc would not be short of oil if Iran stopped crude exports, as they have enough in stock to meet their needs for around 120 days.

Iran continues to flex its military muscle but appears willing to resume talks with world powers. NBC's Ali Arouzi reports.

Industry sources told Reuters on Feb. 16 that Iran's top oil buyers in Europe were making substantial cuts in supply months in advance of European Union sanctions, reducing flows to the continent in March by more than a third - or over 300,000 barrels daily.

France's Total has already stopped buying Iran's crude, which is subject to fresh EU embargoes. Market sources said Royal Dutch Shell has scaled back sharply.

Greece, Turkey and Saudi ArabiaAmong European nations, debt-ridden Greece is most exposed to Iranian oil disruption.

Motor Oil Hellas of Greece was thought to have cut out Iranian crude altogether and compatriot Hellenic Petroleum along with Spain's Cepsa and Repsol were curbing imports from Iran.

Iran was supplying more than 700,000 barrels per day (bpd) to the EU plus Turkey in 2011, industry sources said.

By the start of this year imports had sunk to about 650,000 bpd as some customers cut back in anticipation of an EU ban.

Saudi Arabia says it is prepared to supply extra oil either by topping up existing term contracts or by making rare spot market sales. Iran has criticized Riyadh for the offer.

Iran said the cut will have no impact on its crude sales, warning that any sanctions on its oil will raise international crude prices.